HTML File Does Not Validate - Post ID...

For my love of CoffeeCup, I bought (and installed) the Beta of Website Insight v4 Build 30). One of my better sites under Recommendations >> Moderate "HTML File Does Not Validate". Obviously, I thought this deserved some of my attention. It appears that using itemprop attributes are throwing errors with the W3.org validator.

It appears that HTML5 has forked because itemprop is a valid attribute at WHATWG html.spec.whatwg.org under microdata but not W3? I used the microdata for SEO purposes, for example:

<a itemprop="email" href="mailto:xxx@xxx.com?subject=sales enquiry;body=I want some more information">Email me for more info</a>

So I'm wondering is using microdata attributes hurting or helping from an SEO perspective? If you were me would you remove them from the site or keep them?